1. Field of the Invention
The invention relates to a communication system comprising an ATM network and a demultiplexing device, which device transmits from one of its access points to another access point, information cells formed by a header portion containing an indication of the destination and by a data portion formed by transmit payload, which device comprises:
at least an input access for receiving said cells, PA1 a plurality of output accesses for users, PA1 at least a network circuit which has an input access and comprises a header analyzing element, PA1 a plurality of service circuits to each of which is assigned at least an output access, and PA1 a common line.
The present invention likewise relates to a demultiplexing device, more specifically, for a network of the ATM type.
2. Discussion of the Related Art
ATM networks are used more and more and permit the transmission of large information streams at variable rates to satisfy the different requirements such as made by telephone links and video links. The information streams are transmitted in the form of cells and the demultiplexing devices are to switch each cell they receive on their input access to the correct output access. This task becomes ever more difficult as the number of received cells becomes ever higher.
A demultiplexing device to be used in a communication system of this type which is capable of performing demultiplexing operations is known from French Patent Application Nr. 2,670,972.
This known device is formed by input junction units whose functions may be compared with said network circuits and whose output junction units may be compared with the service circuits.
All the junction units, both output and input junction units, are to have identical characteristic features, because mixing operations are to be carried out for which any input cell of whatever input junction unit can go to the output of whatever output junction unit.
It occurs that users wishing to make use of the services of ATM networks do not need mixer-type devices because these devices often have few input access points for the network compared to the number of output accesses.
A drawback of the known device resides in the fact that the transmit cells are stored twice: a first storage is effected in the input junction unit during the period of time in which the output junction is waited for to be ready to receive the cell destined thereto, and the second storage in the output junction unit during the period of time in which the user device is about to tap the cells. This double storage, in addition to the fact that it implies more equipment, brings along transmission delays which may be annoying to certain applications, for example, the transmission of moving pictures which pictures may not be too jerky on recovery.